This invention relates to a level sensor for insertion in an underground fuel tank. More specifically, it is directed to an improved level sensor offset mounting mechanism that allows convenient incorporation of the level sensor into an existing underground tank.
Large underground fuel tanks, such as those used at gasoline filling stations, typically have a tank fill pipe extending from ground level to a top end of the tank. Within the tank fill pipe, a drop tube extends from ground level to a position near the bottom of the tank. There is a relatively small, set clearance between the tank fill pipe and the drop tube.
Generally, the fuel tanks contain not only fuel but also water. To ensure an adequate supply of fuel, to track the inventory of fuel in the tank, and to determine the leakage from the tank, the levels of both the fuel and the water in the tank must be determined. One type of level sensor, a magnetostrictive level sensor, uses one float that floats at the water level and another float that floats at the fuel level. The position of these floats is determined electronically and transmitted to an instrumentation housing then to a display device.
Presently, the majority of the level sensors and the electrical wiring required to transmit the information to the display device are installed through an unused bung in the top of the tank. Installation of a level sensor in an unused bung requires a disinterring of the tank and subsequent repair of the surface. Disinterring a tank is both expensive and disruptive.
A second method of mounting the level sensor and associated electrical wiring is to install the level sensor through the fill pipe. Mounting of the level sensor through the fill pipe, however, requires installation of a specially designed, slotted drop tube to allow conduit for the level sensor to run therethrough.
One such level sensor that is mounted through the tank fill pipe, utilizes an ultrasonic level measurement device and a collapsible offset mounting mechanism. The collapsible offset mechanism is designed specifically for use with an ultrasonic level measurement device and will not work with a magnetostrictive level sensor because it provides insufficient support. In addition, the collapsible offset mounting mechanism requires a number of parts connected at hinged joints and is, therefore, relatively costly.
Though the above mentioned level sensors may be helpful in measuring the levels within the tank, they can be improved to enable installation in existing tanks through the tank fill pipe. In addition, they can be improved to provide an offset with sufficient support to permit the use of a magnetostrictive level sensor and, at the same time, reduce the number of parts, thereby, reducing the cost and complexity of the offset.